1) The structure determination by single crystal X-ray diffraction of new cytotoxic compounds isolated from marine organisms is planned. Emphasis will be given to compounds with high activity and novel structural type. When it is appropriate, the absolute configuration of the compounds will be determined. Also, the structures of several toxic compounds will be determined. It is anticipated that 10-15 compounds will be investigated each year. 2) The synthesis of large quantities of several self-duplexing nucleotides is planned. Crystallization of these nucleotides and complexes with the double intercalator TANDEM will be attempted. The structure of the nucleotides and complexes will be investigated by X-ray diffraction of single crystals and by NMR of solutions.